5 gallon plant props?

for 5 gallon hydro bucket, I am doing DWC and the damn things are getting too big ;)

my method is I veg for awhile in rubbermaid tubs with 5 inch net pots. When they get 12-24 inches, I take that out, and into a 5 gal net pot it goes. I wind the roots in a circle in a 5 gallon net pot, set the plant all the way on the bottom, and add hydronton on top and the damn things fall over.(coconut is even worse). I grow them tall at 4-6 feet (inc buckets).

am I potting them wrong?

right now, I'm duct taping 5 foot long pvc tubing to the tubs to act as stakes. it's a crappy solution and they need to be retaped, heavy plants pull down the pvc. the duct tape doesn't quite cut it.

it's not a stem problem, it's that the plant moves in the rocks...

also, I have tried putting the plant higher, letting more rocks sit on the root ball. this method was worse for support.